606 research outputs found
X-ray quantum optics with M\"ossbauer nuclei embedded in thin film cavities
A promising platform for the emerging field of x-ray quantum optics are
M\"ossbauer nuclei embedded in thin film cavities probed by near-resonant x-ray
light, as used in a number of recent experiments. Here, we develop a quantum
optical framework for the description of experimentally relevant settings
involving nuclei embedded in x-ray waveguides. We apply our formalism to two
settings of current experimental interest based on the archetype M\"ossbauer
isotope 57Fe. For present experimental conditions, we derive compact analytical
expressions and show that the alignment of medium magnetization as well as
incident and detection polarization enable the engineering advanced quantum
optical level schemes. The model encompasses non-linear and quantum effects
which could become accessible in future experiments.Comment: 13 pages, 6 figure
Collective effects between multiple nuclear ensembles in an x-ray cavity-QED setup
The setting of Moessbauer nuclei embedded in thin-film cavities has
facilitated an aspiring platform for x-ray quantum optics as shown in several
recent experiments. Here, we generalize the theoretical model of this platform
that we developed earlier [Phys. Rev. A 88, 043828 (2013)]. The theory
description is extended to cover multiple nuclear ensembles and multiple modes
in the cavity. While the extensions separately do not lead to qualitatively new
features, their combination gives rise to cooperative effects between the
different nuclear ensembles and distinct spectral signatures in the
observables. A related experiment by Roehlsberger et al. [Nature 482, 199
(2012)] is successfully modeled, the scalings derived with semiclassical
methods are reproduced, and a microscopic understanding of the setting is
obtained with our quantum mechanical description.Comment: 18 pages, 6 figure
Dynamic formation of Rydberg aggregates at off-resonant excitation
The dynamics of a cloud of ultra-cold two-level atoms is studied at
off-resonant laser driving to a Rydberg state. We find that resonant excitation
channels lead to strongly peaked spatial correlations associated with the
buildup of asymmetric excitation structures. These aggregates can extend over
the entire ensemble volume, but are in general not localized relative to the
system boundaries. The characteristic distances between neighboring excitations
depend on the laser detuning and on the interaction potential. These properties
lead to characteristic features in the spatial excitation density, the Mandel
parameter, and the total number of excitations. As an application an
implementation of the three-atom CSWAP or Fredkin gate with Rydberg atoms is
discussed. The gate not only exploits the Rydberg blockade, but also utilizes
the special features of an asymmetric geometric arrangement of the three atoms.
We show that continuous-wave off-resonant laser driving is sufficient to create
the required spatial arrangement of atoms out of a homogeneous cloud.Comment: 8 pages, 7 figure
A hybrid model for Rydberg gases including exact two-body correlations
A model for the simulation of ensembles of laser-driven Rydberg-Rydberg
interacting multi-level atoms is discussed. Our hybrid approach combines an
exact two-body treatment of nearby atom pairs with an effective approximate
treatment for spatially separated pairs. We propose an optimized evolution
equation based only on the system steady state, and a time-independent Monte
Carlo technique is used to efficiently determine this steady state. The hybrid
model predicts features in the pair correlation function arising from
multi-atom processes which existing models can only partially reproduce. Our
interpretation of these features shows that higher-order correlations are
relevant already at low densities. Finally, we analyze the performance of our
model in the high-density case.Comment: significantly expanded and revised version (more observables,
high-density regime); 9 pages, 8 figure
Universal time-evolution of a Rydberg lattice gas with perfect blockade
We investigate the dynamics of a strongly interacting spin system that is
motivated by current experimental realizations of strongly interacting Rydberg
gases in lattices. In particular we are interested in the temporal evolution of
quantities such as the density of Rydberg atoms and density-density
correlations when the system is initialized in a fully polarized state without
Rydberg excitations. We show that in the thermodynamic limit the expectation
values of these observables converge at least logarithmically to universal
functions and outline a method to obtain these functions. We prove that a
finite one-dimensional system follows this universal behavior up to a given
time. The length of this universal time period depends on the actual system
size. This shows that already the study of small systems allows to make precise
predictions about the thermodynamic limit provided that the observation time is
sufficiently short. We discuss this for various observables and for systems
with different dimensions, interaction ranges and boundary conditions.Comment: 16 pages, 3 figure
Ab initio quantum models for thin-film x-ray cavity QED
We develop two ab initio quantum approaches to thin-film x-ray cavity quantum
electrodynamics with spectrally narrow x-ray resonances, such as those provided
by M\"ossbauer nuclei. The first method is based on a few-mode description of
the cavity, and promotes and extends existing phenomenological few-mode models
to an ab initio theory. The second approach uses analytically-known Green's
functions to model the system. The two approaches not only enable one to ab
initio derive the effective few-level scheme representing the cavity and the
nuclei in the low-excitation regime, but also provide a direct avenue for
studies at higher excitation, involving non-linear or quantum phenomena. The ab
initio character of our approaches further enables direct optimizations of the
cavity structure and thus of the photonic environment of the nuclei, to tailor
the effective quantum optical level scheme towards particular applications. To
illustrate the power of the ab initio approaches, we extend the established
quantum optical modeling to resonant cavity layers of arbitrary thickness,
which is essential to achieve quantitative agreement for cavities used in
recent experiments. Further, we consider multi-layer cavities featuring
electromagnetically induced transparency, derive their quantum optical
few-level systems ab initio, and identify the origin of discrepancies in the
modeling found previously using phenomenological approaches as arising from
cavity field gradients across the resonant layers.Comment: 41 pages, 20 figures, added clarifications and minor correction
FUN3D Analyses in Support of the First Aeroelastic Prediction Workshop
This paper presents the computational aeroelastic results generated in support of the first Aeroelastic Prediction Workshop for the Benchmark Supercritical Wing (BSCW) and the HIgh REynolds Number AeroStructural Dynamics (HIRENASD) configurations and compares them to the experimental data. The computational results are obtained using FUN3D, an unstructured grid Reynolds-averaged Navier-Stokes solver developed at NASA Langley Research Center. The analysis results for both configurations include aerodynamic coefficients and surface pressures obtained for steady-state or static aeroelastic equilibrium (BSCW and HIRENASD, respectively) and for unsteady flow due to a pitching wing (BSCW) or modally-excited wing (HIRENASD). Frequency response functions of the pressure coefficients with respect to displacement are computed and compared with the experimental data. For the BSCW, the shock location is computed aft of the experimentally-located shock position. The pressure distribution upstream of this shock is in excellent agreement with the experimental data, but the pressure downstream of the shock in the separated flow region does not match as well. For HIRENASD, very good agreement between the numerical results and the experimental data is observed at the mid-span wing locations
Lessons Learned in the Selection and Development of Test Cases for the Aeroelastic Prediction Workshop: Rectangular Supercritical Wing
The Aeroelastic Prediction Workshop brought together an international community of computational fluid dynamicists as a step in defining the state of the art in computational aeroelasticity. The Rectangular Supercritical Wing (RSW) was chosen as the first configuration to study due to its geometric simplicity, perceived simple flow field at transonic conditions and availability of an experimental data set containing forced oscillation response data. Six teams performed analyses of the RSW; they used Reynolds-Averaged Navier-Stokes flow solvers exercised assuming that the wing had a rigid structure. Both steady-state and forced oscillation computations were performed by each team. The results of these calculations were compared with each other and with the experimental data. The steady-state results from the computations capture many of the flow features of a classical supercritical airfoil pressure distribution. The most dominant feature of the oscillatory results is the upper surface shock dynamics. Substantial variations were observed among the computational solutions as well as differences relative to the experimental data. Contributing issues to these differences include substantial wind tunnel wall effects and diverse choices in the analysis parameters
Tunable sub-luminal propagation of narrowband x-ray pulses
Group velocity control is demonstrated for x-ray photons of 14.4 keV energy
via a direct measurement of the temporal delay imposed on spectrally narrow
x-ray pulses. Sub-luminal light propagation is achieved by inducing a steep
positive linear dispersion in the optical response of Fe M\"ossbauer
nuclei embedded in a thin film planar x-ray cavity. The direct detection of the
temporal pulse delay is enabled by generating frequency-tunable spectrally
narrow x-ray pulses from broadband pulsed synchrotron radiation. Our
theoretical model is in good agreement with the experimental data.Comment: 8 pages, 4 figure
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